1. Field of The Invention
The invention relates to a receiver comprising a tunable parallel resonant circuit which is coupled to an input of a transistor circuit via a coupling network including a coupling capacitor.
2. Description of The Related Art
Philips television (TV) tuners of the type UV816 include a tunable bandpass filter which can be tuned throughout the VHF-low band ranging, for example, from 48 to 168 MHz. The tunable bandpass filter is coupled between a radio-frequency (RF) input amplifier and a mixer circuit which forms part of an integrated circuit. It comprises two parallel resonant circuits which are mutually coupled. One of the two parallel resonant circuits is coupled to the RF input amplifier. The other resonant circuit is coupled to an input transistor of the mixer circuit via a coupling network including a coupling capacitor and a varicap diode of the type BB131. A tuning voltage is applied to the varicap diode so as to vary its capacitance throughout the VHF-low band.
In the background art, it is essential that the coupling network includes the varicap diode to which the tuning voltage is applied. If the varicap had not been present, the background-art tuner would have suffered from relatively poor signal-handling in terms of noise and gain. Moreover, the tunable parallel resonant circuit would not have been tuned sufficiently correctly throughout the relevant frequency band, which is the VHF-low band, as a result of a tracking error with an oscillator resonant circuit in the background-art tuner.